Given below are two statements :
Statement I : The structure of Maltose is given below:
Statement II : The structure of Lactose is given below :
In the light of the above statements, choose the correct answer from the options given below :

Solution

Chemistry ma’am · 3 steps

Look for a free OH on an anomeric carbon: if one is left, the sugar is reducing.

1. Reducing sugar test. A disaccharide is reducing if one of its anomeric carbons (C1 of glucose or galactose) still carries a free OH. That hemiacetal ring can open to a free CHO group, which reduces Tollens' and Fehling's reagents.
2. Read both drawings. Both structures are drawn correctly. Each has the C1 of the left ring joined through O to C4 of the right ring, so the right ring keeps a free OH at its C1. The only thing to check is the label printed beside each structure.

   Sugar	Linkage	Free OH at an anomeric C?	Label given	Verdict
   Maltose	α-D-glucose C1 to C4 of D-glucose	Yes, on C1 of the second glucose	non-reducing	False: maltose is reducing
   Lactose	β-D-galactose C1 to C4 of D-glucose	Yes, on C1 of the glucose unit	reducing	True

3. So. Statement I is false, because maltose is a reducing sugar. Statement II is true. The answer is (d).

The idea to keep. Only sucrose among the common disaccharides is non-reducing, because its C1–C2 link ties up both anomeric carbons. Maltose and lactose use a 1→4 link and keep one free hemiacetal OH, so both are reducing.

Answer from the NTA final answer key. Solution by PrepWiser.